Injection molded body having excellent barrier property

ABSTRACT

The present invention relates to a multilayer injection molded article comprising a layer of a barrier resin composition including (A) 10 to 70% by mass of a polyamide resin including a diamine constitutional unit 70 mol % or more of which is derived from m-xylylenediamine and a dicarboxylic acid constitutional unit 70 mol % or more of which is derived from a dicarboxylic acid containing a C 4  to C 20  α,ω-linear aliphatic dicarboxylic acid and isophthalic acid at a molar ratio of from 30:70 to 100:0, (B) 90 to 30% by mass of a modified polyolefin, and the like; a multilayer injection molded article including a layer of a barrier resin composition including (A) 50 to 90% by mass of the above polyamide resin, (B) 2 to 45% by mass of the modified polyolefin and (D) 2 to 45% by mass of a m-xylylene group-free polyamide; and an injection molded article including (A) 10 to 60% by mass of the polyamide resin and (E) 40 to 90% by mass of a polyolefin wherein at least a part of the polyamide (A) is dispersed in a layered state. These molded articles are excellent in barrier property.

TECHNICAL FIELD

The present invention relates to injection-molded articles havingexcellent barrier property and appearance, etc., and more particularlyto multilayer injection molded articles that are excellent in barrierproperty, appearance, delamination resistance, heat resistance, etc.,and single-layer injection-molded articles that are excellent in barrierproperty, appearance, etc.

BACKGROUND ART

Injection molding has been widely spread and used in variousapplications such as mechanical parts, automobile parts, electric andelectronic parts and containers for food and drugs because it is capableof producing molded articles having a complicated shape with a highproductivity. In particular, containers for beverages, etc., have beenfrequently constructed from an injection molded article because a mouthportion of these containers is formed into an excellent threaded shapein order to ensure sufficient tightening of a cap thereon.

As the material for injection molding articles, there have been usedvarious general resins including polyolefins such as polyethylene andpolypropylene, polyesters and polystyrenes. Of these resins, polyolefinssuch as polypropylene have been extensively used in various applicationssuch as containers because they are excellent in flowability and heatresistance upon molding as well as exhibit a light weight and a lowmoisture absorption and are available at low costs.

However, the polyolefins tend to be deteriorated in barrier propertyagainst gases such as oxygen and are, therefore, unsuitable ascontainers for preserving contents that are apt to be adversely affectedby oxygen, etc., or as containers for food or drugs which are requiredto exhibit a good keeping property under severe environmental conditionssuch as high-temperature conditions. In consequence, there are disclosedmethods in which a barrier material such as polyamides is blended in thepolyolefins to improve a barrier property of the polyolefins (refer toPatent Documents 1 and 2).

These methods might improve a barrier property of the polyolefins tosome extent. However, the barrier material to be blended must bedispersed in the polyolefins in a specific condition, so that thepolyolefins tend to be improved in barrier property only to aninsufficient extent. In addition, these methods also have such a problemthat molded articles obtained from the resin mixture tend to have a poorappearance owing to the polyamides that are locally present near asurface thereof. More specifically, the method of the Patent Document 1requires a biaxial stretch blow molding procedure, and the moldedarticles obtained without conducting the biaxial stretch blow moldingprocedure tend to be deteriorated in barrier property. Whereas, thePatent Document 2 discloses the composite molded article made of apolyolefin matrix and an amorphous polyamide in the form of a pluralityof masses dispersed in the polyolefin, but is silent about crystallinepolyamides and polyamides having a m-xylylene skeleton.

Upon producing a molded article having a multilayer structure includingpolyolefin layers and a barrier layer by injection molding method, sincea material for the barrier layer exhibit no adhesion to the polyolefinlayers, the molded article is required to have, for example, a structurehaving at least five layers, i.e., a layer structure of polyolefinlayer/adhesive layer/barrier layer/adhesive layer/polyolefin layer. Theproduction of the molded article having such a multilayer structuretends to be accompanied with difficulties in view of its structure andmoldability and, therefore, has been rarely practiced from industrialviewpoints. In consequence, there is disclosed a method in which apolyolefin is compounded with a modified polyolefin to enhance adhesionof a polyolefin layer to a barrier layer and necessitate no adhesivelayer therebetween (refer to Patent Document 3). The method of thePatent Document 3 improves adhesion between the polyolefin layer andbarrier layer, but requires a large amount of the expensive modifiedpolyolefin to ensure sufficient adhesion between these layers. Inaddition, this method has such a problem that the resulting moldedarticle tends to be deteriorated in heat resistance owing to addition ofthe modified polyolefin thereto.

The present inventors have previously proposed the polyamide resinobtained by polycondensation of a diamine component containing 70 mol %or more of m-xylylenediamine and a mixed dicarboxylic acid componentcontaining an α,ω-linear aliphatic dicarboxylic acid and isophthalicacid (refer to Patent Document 4). The polyamide resin exhibits anexcellent barrier property. However, it has been still required that amultilayer injection molded article produced using the polyamide resinis further improved in delamination resistance.

Patent Document 1: JP 2004-292037A

Patent Document 2: JP 2005-8664A

Patent Document 3: JP 2006-131275A

Patent Document 4: JP 2004-352985A

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

An object of the present invention is to solve the above conventionalproblems encountered in containers obtained by injection molding, andprovide a multilayer injection molded article that is excellent inbarrier property, appearance, delamination resistance and heatresistance, as well as a single-layer injection molded article that isexcellent in barrier property, appearance, etc., which is capable ofbeing produced in an economically advantageous manner.

Means for Solving the Problem

As the result of extensive and intensive researches for achieving theabove object, the present inventors have found that the object issuitably achieved by a multilayer injection molded article including aresin layer composed of a specific polyamide resin and a modifiedpolyolefin or a resin layer composed of the polyamide resin, themodified polyolefin and the other polyamide resin as a barrier layer, orby an injection molded article in which the above specific polyamideresin is dispersed in a layered state in a mixed polyolefin. The presentinvention has been accomplished on the basis of the above finding.

Thus, the present invention relates to the injection molded articles asdescribed in the following aspects.

1. An injection molded article with a multilayer structure including atleast one layer of a barrier resin composition including (A) 10 to 70%by mass of a polyamide resin including a diamine constitutional unit 70mol % or more of which is derived from m-xylylenediamine and adicarboxylic acid constitutional unit 70 mol % or more of which isderived from a dicarboxylic acid containing a C₄ to C₂₀ α,ω-linearaliphatic dicarboxylic acid and isophthalic acid at a molar ratio offrom 30:70 to 100:0; (B) 90 to 30% by mass of a modified polyolefin; and(C) 0 to 50% by mass of a polyolefin.

2. An injection molded article with a multilayer structure including atleast one layer of a barrier resin composition including (A) 50 to 90%by mass of a polyamide resin including a diamine constitutional unit 70mol % or more of which is derived from m-xylylenediamine and adicarboxylic acid constitutional unit 70 mol % or more of which isderived from a dicarboxylic acid containing a C₄ to C₂₀ α,ω-linearaliphatic dicarboxylic acid and isophthalic acid at a molar ratio offrom 30:70 to 100:0; (B) 2 to 45% by mass of a modified polyolefin; and(D) 2 to 45% by mass of a m-xylylene group-free polyamide (D).

3. An injection molded article including (A) 10 to 60% by mass of apolyamide resin including a diamine constitutional unit 70 mol % or moreof which is derived from m-xylylenediamine and a dicarboxylic acidconstitutional unit 70 mol % or more of which is derived from adicarboxylic acid containing a C₄ to C₂₀ α,ω-linear aliphaticdicarboxylic acid and isophthalic acid at a molar ratio of from 30:70 to100:0; and (E) 40 to 90% by mass of a mixed polyolefin including (C) 40to 100% by mass of a polyolefin and (B) 0 to 60% by mass of a modifiedpolyolefin, wherein at least a part of the polyamide resin (A) isdispersed in a layered state.

4. The injection molded article according to the above aspect 1 or 2,wherein the polyamide resin (A) has a relative viscosity of 2.5 or moreas measured at 25° C. in 96% by mass concentrated sulfuric acid as asolvent with a concentration of 1 g/100 mL.

5. The injection molded article according to any one of the aboveaspects 1 to 3, wherein the modified polyolefin (B) is obtained bygraft-modifying the polyolefin (C) with an unsaturated carboxylic acidor an anhydride thereof.

6. The injection molded article according to the above aspect 2, whereinthe m-xylylene group-free polyamide (D) is an aliphatic polyamideselected from the group consisting of nylon-6, nylon-66 and nylon-666.

7. The injection molded article according to the above aspect 2, whereinthe m-xylylene group-free polyamide (D) is an aliphatic polyamide havinga relative viscosity of less than 5 as measured at 25° C. in 96% by massconcentrated sulfuric acid as a solvent with a concentration of 1 g/100mL.

8. The injection molded article according to the above aspect 1 or 2,wherein the article has a multilayer structure in which the layer of thebarrier resin composition is sandwiched between thermoplastic resinlayers (F) each made of a polyolefin.

9. The injection molded article according to the above aspect 1 or 2,wherein the article is in the form of a multilayer stretched injectionmolded article obtained by subjecting a multilayer injection moldedarticle to biaxial stretch blow molding.

Effect of the Invention

The injection molded article with a multilayer structure according tothe above aspect 1 of the present invention (hereinafter occasionallyreferred to merely as the “multilayer injection molded article I”) andthe injection molded article with a multilayer structure according tothe above aspect 2 of the present invention (hereinafter occasionallyreferred to merely as the “multilayer injection molded article II”) areexcellent in barrier property, delamination resistance, heat resistanceand appearance. In particular, the multilayer injection molded articlesI and II are prevented from suffering from delamination between abarrier resin layer and adjacent layers even when exposed to severeimpact upon transportation or drop thereof, are capable of avoidingoccurrence of the delamination even though they are not formed into sucha shape having less irregular and flexed portions, and therefore exhibita large freedom of design.

The injection molded article according to the above aspect 3 of thepresent invention (hereinafter occasionally referred to merely as the“single-layer injection molded article”) is excellent in barrierproperty and appearance, and can be produced in an economicallyadvantageous manner.

Therefore, the multilayer injection molded articles I and II and thesingle-layer injection molded article are suitably used as containersfor liquid food such as beverages and soups or for food and drugscapable of being subjected to retort treatment, etc.

BEST MODE FOR CARRYING OUT THE INVENTION

The polyamide resin (A) used in the multilayer injection molded articlesI and II and the single-layer injection molded article according to thepresent invention includes a diamine constitutional unit and adicarboxylic cid constitutional unit in which 70 mol % or more of thediamine constitutional unit is derived from m-xylylenediamine, and 70mol % or more of the dicarboxylic acid constitutional unit is derivedfrom a dicarboxylic acid containing a C₄ to C₂₀ α,ωlinear aliphaticdicarboxylic acid and isophthalic acid at a molar ratio of from 30:70 to100:0.

The multilayer injection molded articles I and II of the presentinvention includes at least one layer of a barrier resin compositioncontaining the polyamide resin (A) as a main component, and preferablyhas such a multilayer structure in which the layer of the barrier resincomposition is sandwiched between thermoplastic resin layers (E) eachmade of a polyolefin.

The single-layer injection molded article of the present invention hassuch a structure in which at least a part of the polyamide resin (A) isdispersed in a layered state in a molded body containing a polyolefin(C).

Examples of diamines other than m-xylylenediamine which may be used as araw material for production of the polyamide resin (A) include aliphaticdiamines such as tetramethylenediamine, pentamethylenediamine, 2-methylpentanediamine, hexamethylenediamine, heptamethylenediamine,octamethylenediamine, nonamethylenediamine, decamethylenediamine,dodecamethylenediamine, 2,2,4-trimethyl-hexamethylenediamine and2,4,4-trimethyl-hexamethylenediamine; alicyclic diamines such as1,3-bis(aminomethyncydohexane, 1,4-bis(aminomethyl)cyclohexane,1,3-diaminocyclohexane, 1,4- diaminocyclohexane, bis(4-aminocyclohexyl)methane, 2,2-bis(4-aminocyclohexyl)propane,bis(aminomethyl)decalin (including structural isomers thereof) andbis(aminomethyl)tricyclodecane (including structural isomers thereof);and aromatic ring-containing diamines such as bis(4-aminophenyl)ether,p-phenylenediamine, p-xylylenediamine and bis(aminomethyl)naphthalene.These diamines other than m-xylylenediamine may be used in an amount of30 mol % or less on the basis of the whole diamine components.

Examples of the C₄ to C₂₀ α,ω-linear aliphatic dicarboxylic acid includealiphatic dicarboxylic acids such as succinic acid, glutaric acid,pimelic acid, suberic acid, azelaic acid, adipic acid, sebacic acid,undecanedioic acid and dodecandioic acid. Of these acids, especiallypreferred is adipic acid.

The molar ratio of the C₄ to C₂₀ α,ω-linear aliphatic dicarboxylic acidto isophthalic acid in the mixed dicarboxylic acid is from 30:70 to100:0, preferably from 30:70 to 95:5, more preferably from 40:60 to 95:5and still more preferably from 60:40 to 90:10. When using the mixeddicarboxylic acid containing isophthalic acid in the above specifiedrange, the resulting polyamide resin is enhanced in barrier property. Inaddition, the polyamide resin produced by using the mixed dicarboxylicacid not only has a lower melting point, is shaped at a lowertemperature, and is therefore capable of being produced with a lessenergy and shortened in molding cycle, but also exhibits a higher meltviscosity and is therefore improved in moldability without occurrence ofdrawdown of the resin, etc., as compared to the polyamide resin producedfrom the C₄ to C₂₀ α,ω-linear aliphatic dicarboxylic acid solely.

Examples of dicarboxylic acids other than the C₄ to C₂₀ α,ω-linearaliphatic dicarboxylic acid and isophthalic acid which may be used as adicarboxylic acid component of the polyamide resin (A) in the presentinvention include phthalic acid compounds such as terephthalic acid andorthophthalic acid; naphthalenedicarboxylic acids such as1,2-naphthalenedicarboxylic acid, 1,3-naphthalenedicarboxylic acid,1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 1,6-naphthalenedicarboxylic acid, 1,7-naphthalenedicarboxylic acid, 1,8naphthalenedicarboxylic acid, 2,3-naphthalenedicarboxylic acid,2,6-naphthalenedicarboxylic acid and 2,7-naphthalenedicarboxylic acid;monocarboxylic acids such as benzoic acid propionic acid and butyricacid; polycarboxylic acids such as trimellitic acid and pyromelliticacid; carboxylic acid anhydrides such as trimellitic anhydride andpyromellitic anhydride.

In the polyamide resin (A) used in the present invention, the content ofthe constitutional unit derived from these dicarboxylic acids other thanthe C₄ to C₂₀ α,ω-linear aliphatic dicarboxylic acid and isophthalicacid is in the range of 30 mol % or less on the basis of the wholedicarboxylic acid constitutional units.

The polyamide resin (A) is produced by polycondensing a diaminecomponent containing m-xylylenediamine in an amount of 70 mol % or morewith a dicarboxylic acid component containing the mixed dicarboxylicacid composed of the C₄ to C₂₀ α,ω-linear aliphatic dicarboxylic acidand isophthalic acid at a molar ratio of from 30:70 to 100:0, in anamount of 70 mol % or more. The production method is not particularlylimited. The polyamide resin (A) may be produced by conventionally knownmethods such as atmospheric melt polymerization and pressure meltpolymerization.

For example, the polyamide resin (A) may be produced by heating a nylonsalt produced from m-xylylenediamine and adipic acid or fromm-xylylenediamine, adipic acid and isophthalic acid under pressure inthe presence of water, and polymerizing the nylon salt while being keptin a molten state and removing water added and condensed water produced,from the reaction system. Alternatively, the polyamide resin (A) may beproduced by directly adding m-xylylenediamine to adipic acid or amixture of adipic acid and isophthalic acid which is kept in a moltenstate, and polycondensing these compounds with each other under normalpressures. In the latter method, in order to prevent the reaction systemfrom being solidified, m-xylylenediamine is continuously added to thedicarboxylic acid component, and the polycondensation reactiontherebetween proceeds while heating the reaction system to keep thereaction temperature during the addition at such a temperature not lowerthan melting points of oligoamides and polyamides produced.

Upon the polycondensation for production of the polyamide resin (A),lactams such as ε-caprolactam, ω-laurolactam and ω-enanthlactam, aminoacids such as 6-aminocaproic acid, 7-aminoheptanoic acid,11-aminoundecanoic acid, 12-aminododecanoic acid, 9-aminononanoic acidand p-aminomethylbenzoic acid, etc., may be added to thepolycondensation reaction system unless the addition thereof adverselyaffects the properties of the obtained polyamide resin.

The polyamide resin (A) is preferably further subjected to heattreatment after the above polycondensation to enhance a melt viscositythereof. The heat treatment may be conducted, for example, by a methodin which the polyamide resin is gently heated in the presence of waterin an inert gas atmosphere or under reduced pressure using a batch typeheater such as a rotary drum and crystallized while avoiding fusionthereof, followed by subjecting the resulting resin to further heattreatment; a method in which the polyamide resin is heated andcrystallized in an inert gas atmosphere using a groove type stirringheater, and then the resulting resin is heat-treated in an inert gasatmosphere using a hopper-shaped heater; or a method in which thepolyamide resin is crystallized using a groove type stirring heater, andthen the resulting resin is heat-treated using a batch type heater suchas a rotary drum. Among these methods, preferred is the method in whichthe crystallization and heat treatment are conducted using the batchtype heater. The conditions of the treatments are preferably controlledsuch that the polyamide resin (A) obtained by the melt polymerization isheated from 70° C. to 120° C. over 0.5 to 4 h in the presence of waterin an amount of 1 to 30% by mass based on the polyamide resin andcrystallized, and then further heat-treated at a temperature of from[melting point of polyamide resin (A)—50° C.] to [melting point ofpolyamide resin (A)—10° C.] over 1 to 12 h in an inert gas atmosphere orunder reduced pressure.

The polyamide resin (A) used in the multilayer injection molded articlesI and II preferably has a relative viscosity of 2.5 or more and morepreferably 3 or more as measured at 25° C. in 96% by mass concentratedsulfuric acid as a solvent with a concentration of 1 g/100 mL. When therelative viscosity of the polyamide resin (A) is less than 2.5, thepolyamide resin (A) tends to be insufficient in adhesion property,thereby causing delamination of the resulting article.

The polyamide resin (A) used in the single-layer injection moldedarticle preferably has a relative viscosity of 2.5 or less and morepreferably 2.3 or less as measured under the same conditions asdescribed above. When the relative viscosity of the polyamide resin (A)is more than 2.5, the polyamide resin (A) tends to be insufficient inbarrier property.

The melting point of the polyamide resin (A) used in the multilayerinjection molded articles I and II and the single-layer injection moldedarticle of the present invention is preferably controlled to atemperature range of from 160 to 240° C., more preferably from 170 to235° C. and still more preferably from 180 to 230° C.

Meanwhile, when the melting point of the polyamide resin (A) used in themultilayer injection molded article I is controlled to be close to themelting point of the modified polyolefin (B) or the polyolefin (C), itis possible to prevent occurrence of defects such as unevenness inthickness owing to difference in molding temperature between resins uponproduction of the multilayer molded article, or suppress generation ofoff-odor and undesirable coloration owing to deterioration of theresins.

In addition, when the melting point of the polyamide resin (A) used inthe multilayer injection molded article II is controlled to be close tothe melting point of the thermoplastic resin (F) used for sandwichingthe layer of the barrier resin composition between layers thereof, it isalso possible to prevent occurrence of defects such as unevenness inthickness owing to difference in molding temperature between resins uponproduction of the multilayer molded article, or suppress generation ofoff-odor and undesirable coloration owing to deterioration of theresins.

The glass transition point of the polyamide resin (A) is preferably inthe range of from 80 to 130° C. The polyamide having a glass transitionpoint of 80° C. or higher exhibits an excellent barrier property under ahigh temperature condition.

The polyamide resin (A) suitably used in the present invention has anend amino group concentration of less than 40 μ-equivalent/g, preferablyfrom 10 to 30 μ-equivalent/g, and more preferably a carboxyl groupconcentration of from 40 to 100 μ-equivalent/g or more. When controllingthe end amino group concentration of the polyamide resin (A) to theabove specified range, the resulting barrier layer can be prevented fromsuffering from yellow discoloration.

The polyamide resin (A) preferably contains a phosphorus compound inorder to enhance a processing stability upon melt molding or preventundesirable coloration of the polyamide resin. As the phosphoruscompound, there may be suitably used those phosphorus compoundscontaining an alkali metal or an alkali earth metal. Examples of thephosphorus compound include phosphates, hypophosphites and phosphites ofsodium, magnesium, calcium, etc. Among these phosphorus compounds,hypophosphites of the alkali metal or alkali earth metal are preferablyused because of an excellent anti-coloring effect for polyamides. Theconcentration of the phosphorus compound in the polyamide resin (A) is200 ppm or less, preferably 160 ppm or less and more preferably 100 ppmor less in terms of phosphorus atom.

Meanwhile, the polyamide resin (A) may also contain, in addition to theabove phosphorus compound, various additives such as lubricants,delustering agents, heat stabilizers, weather stabilizers, ultravioletabsorbers, nucleating agents, plasticizers, flame retardants, antistaticagents, anti-coloring agents and anti-gelling agents, unless theaddition thereof adversely affects the aimed effects of the presentinvention. Further, various materials, though not particularly limitedto those previously described, may be mixed in the polyamide resin (A).

The polyamide resin (A) is preferably dried before used to such anextent that a water content thereof is reduced to 0.10% by mass or less,preferably 0.08% by mass or less and more preferably 0.05% by mass orless. The polyamide resin (A) having a water content of 0.10% by mass orless is free from formation of air bubbles owing to water vaporgenerated therefrom upon melt-mixing with other components. Thepolyamide resin (A) may be dried by known methods. For example, theremay be adopted such a method in which the polyamide resin (A) is chargedinto a heatable tumbler equipped with a vacuum pump (rotary vacuumvessel) or a pressure-reduced dryer, and heated and dried at atemperature not higher than a melting point of the polymer andpreferably not higher than 160° C. under reduced pressure.

The modified polyolefin (B) suitably used in the present invention isobtained by graft-modifying the polyolefin (C) with an unsaturatedcarboxylic acid or an anhydride thereof.

The polyolefin (C) used in the present invention includes variouspolyolefins. Examples of the suitable polyolefin include homopolymers ofethylenically unsaturated hydrocarbons having 2 or more carbon atoms andpreferably 2 to 8 carbon atoms such as low-density polyethylene,medium-density polyethylene, high-density polyethylene, linearlow-density polyethylene, polypropylene, 1-polybutene and 1-polymethylpentene; homopolymers of α-olefins having 3 to 20 carbon atoms;copolymers of α-olefins having 3 to 20 carbon atoms (such asethylene-propylene copolymers, ethylene-propylene-diene terpolymers,ethylene-1-butene copolymers, ethylene-4-methyl-1-pentene copolymers,ethylene-1-hexene copolymers, ethylene-1-octene copolymers,ethylene-1-decene copolymers, propylene-1-butene copolymers,propylene-4-methyl-1-pentene copolymers, propylene-1-hexene copolymers,propylene-1-octene copolymers and propylene-1-decene copolymers); andcopolymers of an α-olefin having 3 to 20 carbon atoms with a cyclicolefin (such as copolymers of an α-olefins having 3 to 20 carbon atomswith norbornene). These polyolefins may be used singly or in the form ofa mixture of any two or more thereof.

Among these polyolefins, preferred are polyethylene, polypropylene,1-polybutene, and resins having a high glass transition point such asthe copolymers of an α-olefin with a cyclic olefin, and more preferredis polypropylene because it is excellent in heat resistance.

The polyolefin (C) used in the present invention preferably has a meltflow rate (MFR) of from 1 to 100 g/10 min as measured at 190° C. under aload of 2.16 kgf. When using the polyolefin (C) having a MFR of 1 g/10min or more, the resulting molded article is free from molding defectssuch as unevenness in thickness.

As described above, the modified polyolefin (B) used in the presentinvention is obtained by graft-modifying the above polyolefin (C) withan unsaturated carboxylic acid or an anhydride thereof, and may besuitably selected from those generally extensively used ascompatibilizers or adhesives.

Specific examples of the unsaturated carboxylic acid or anhydridethereof include acrylic acid, methacrylic acid, a-ethyl acrylic acid,maleic acid, fumaric acid, itaconic acid, citraconic acid,tetrahydrophthalic acid, chloromaleic acid, butenyl succinic acid andanhydrides of these acids. Among these acids and anhydrides, preferredare maleic acid and maleic anhydride.

As the method of obtaining the modified polyolefin (B) bygraft-copolymerizing the polyolefin with the unsaturated carboxylic acidor anhydride thereof, there my be used various conventionally knownmethods. For example, there may be used a method of melting thepolyolefin using an extruder, etc., and then adding a monomer to begrafted to the molten polyolefin to copolymerize the polyolefintherewith; a method of dissolving the polyolefin in a solvent and thenadding a monomer to be grafted to the resulting solution to copolymerizethe polyolefin therewith; and a method of suspending the polyolefin inwater and then adding a monomer to be grafted to the resultingsuspension to copolymerize the polyolefin therewith.

Examples of the thus graft-modified polyolefin (B) include “MODICAP-P502” and “MODIC AP-P565” (all available from Mitsubishi ChemicalCorp.), “ADMER GT6” available from Mitsui Chemical Corp., and “ADTEXDU0500” available from Nippon Polyethylene Co., Ltd.

The modified polyolefin (B) used in the present invention preferably hasa melt flow rate (MFR) of from 0.5 to 50 g/10 min as measured at 190° C.under a load of 2.16 kgf. When controlling the MFR of the modifiedpolyolefin (B) to the above specified range, the resulting resinexhibits excellent adhesion property and moldability.

The layer of the barrier resin composition for the multilayer injectionmolded article I is obtained by mixing the polyamide resin (A), themodified polyolefin (B) and the polyolefin (C) with each other. Thebarrier resin composition for the multilayer injection molded article Icontains 10 to 70% by mass of the polyamide resin (A), 90 to 30% by massof the modified polyolefin (B) and 0 to 50% by mass of the polyolefin(C), preferably contains 15 to 65% by mass of the component (A), 85 to35% by mass of the component (B) and 0 to 40% by mass of the component(C), and more preferably contains 20 to 60% by mass of the component(A), 80 to 40% by mass of the component (B) and 0 to 30% by mass of thecomponent (C). When adjusting the content of the component (A) to 10% bymass or more, the resulting resin composition exhibits a sufficientbarrier property, and when adjusting the content of the component (A) to70% by mass or less, the resulting layer exhibits a sufficient adhesionto the adjacent layers. In addition, when adjusting the content of thecomponent (B) to 30% by mass or more, the resulting resin compositionexhibits a sufficient adhesion property, and when adjusting the contentof the component (B) to 90% by mass or less, the resulting resincomposition exhibits a sufficient barrier property. Further, whenadjusting the content of the component (C) to 50% by mass or less, theresulting resin composition exhibits a sufficient adhesion property.

The layer of the barrier resin composition for the multilayer injectionmolded article II is obtained by mixing the polyamide resin (A), themodified polyolefin (B) and the m-xylylene group-free polyamide (D) witheach other. The barrier resin composition for the multilayer injectionmolded article II contains 50 to 90% by mass of the polyamide resin (A),2 to 45% by mass of the modified polyolefin (B) and 2 to 45% by mass ofthe m-xylylene group-free polyamide (D), and preferably contains 55 to85% by mass of the component (A), 5 to 40% by mass of the component (B)and 5 to 40% by mass of the component (D).

The m-xylylene group-free polyamide (D) is preferably softer than thepolyamide resin (A). Examples of the m-xylylene group-free polyamide (D)include aliphatic polyamides such as nylon-4, nylon-6, nylon-12,nylon-66, nylon-46, nylon-610, nylon-612 and nylon-666 (copolymer ofnylon-6 with nylon-66). Among these aliphatic polyamides, preferred arenylon-6, nylon-66 and nylon-666.

When adjusting the content of the component (A) in the barrier resincomposition containing the m-xylylene group-free polyamide (D) to 50% bymass or more, the resulting resin composition exhibits a sufficientbarrier property, whereas when adjusting the content of the component(A) in the barrier resin composition containing the m-xylylenegroup-free polyamide (D) to 90% by mass or less, the resulting layerexhibits a sufficient adhesion to the adjacent layers. In addition, whenadjusting the content of the component (B) in the barrier resincomposition containing the m-xylylene group-free polyamide (D) to 20% bymass or more, the resulting resin composition exhibits a sufficientadhesion property, whereas when adjusting the content of the component(B) in the barrier resin composition containing the m-xylylenegroup-free polyamide (D) to 45% by mass or less, the resulting resincomposition exhibits a sufficient barrier property.

The m-xylylene group-free polyamide (D) preferably has a relativeviscosity of less than 5 and more preferably less than 4 as measured at25° C. in 96% by mass concentrated sulfuric acid as a solvent with aconcentration of 1 g/100 mL. When adjusting the relative viscosity ofthe m-xylylene group-free polyamide (D) to less than 5, the resultingresin composition is free from problems such as variation in extrusionoutput or breaking of strands extruded upon being premixed in anextruder.

Meanwhile, the relative viscosity of the m-xylylene group-free polyamide(D) is determined as follows. That is, one gram of the m-xylylenegroup-free polyamide (D) is accurately weighed, and dissolved in 100 mLof 96% by mass sulfuric acid at a temperature of 20 to 30° C. whilestirring. After completely dissolving the m-xylylene group-freepolyamide (D) in the acid, 5 cc of the resulting solution is rapidlysampled and placed in a Canon Fenske viscometer. After the viscometerfilled with the polyamide solution is allowed to stand in a constanttemperature oven maintained at 25° C. for 10 min, a dropping time (t) ofthe solution is measured. Also, a dropping time (t₀) of the 96% by masssulfuric acid solely is measured. The relative viscosity of them-xylylene group-free polyamide (D) is calculated from the thus measureddropping times t and t₀ according to the following formula:

Relative Viscosity=(t)/(t ₀)

As described above, the multilayer injection molded articles I and II ofthe present invention include at least one layer of the barrier resincomposition which is preferably sandwiched between of thermoplasticresin layers (F).

The respective thermoplastic resin layers (F) may be formed from variousthermoplastic resins, preferably from polyolefins. Examples of thepolyolefins used for production of the thermoplastic resin layers (F)between which the layer of the barrier resin composition is sandwichedinclude linear low-density polyethylene, low-density polyethylene,medium-density polyethylene, high-density polyethylene, ultrahighmolecular weight high-density polyethylene, polypropylene, copolymers oftwo or more kinds of olefins selected from ethylene, propylene, butene,etc., and mixtures of these compounds. Among these polyolefins,polypropylene is especially preferred because of excellent heatresistance thereof. In addition, the polyolefins for the thermoplasticresin layers (F) may be used in the form of a mixture with the otherresins such as elastomers, or a mixture with the other additives suchas, for example, carbon black and flame retardants.

The multilayer injection molded articles I and II of the presentinvention may be produced, for example, in the following manner. Usingan injection molding machine having two injection cylinders, thethermoplastic resin and the barrier resin composition are injected froma skin-side injection cylinder and a core-side injection cylinder,respectively, through mold hot runners into a mold cavity to obtain amultilayer body. Further, the thus obtained multilayer injection moldedarticle is subjected to biaxial stretch blow molding to obtain amultilayer stretched injection molded article. The biaxial stretch blowmolding of the multilayer injection molded article may be conducted byconventionally known methods. For example, there may be adopted themethod in which the multilayer injection molded article is heated to atemperature of 120 to 170° C. as measured on its surface, and thensubjected to blow molding. The blow pressure used in the above method isusually from 1 to 4 MPa.

According to the above method, in the step of injecting thethermoplastic resin such as polyolefins which forms innermost andoutermost layers through the skin-side injection cylinder and injectingthe barrier resin composition which forms the barrier layer through thecore-side injection cylinder, the thermoplastic resin is first injectedand then the barrier resin composition is injected, and further anecessary amount of the thermoplastic resin is injected to fully fillthe mold cavity, thereby producing a multilayer injection molded articlehaving a three-layer structure (thermoplastic resin/barrier resincomposition/thermoplastic resin). Meanwhile, the method of producing themultilayer parison is not particularly limited to the above method.

The average thickness of the respective thermoplastic resin layers (F)in the multilayer injection molded articles I and II is preferably from0.01 to 3.0 mm. The average thickness of the layer of the barrier resincomposition in the multilayer injection molded articles I and II ispreferably from 0.005 to 2 mm. The wall thickness of a multilayercontainer constituted from the multilayer injection molded articles I orII is not necessarily kept constant over an entire part thereof, and theaverage wall thickness of the multilayer container is usually from 0.01to 5.0 mm.

The multilayer injection molded articles I and II produced according tothe present invention may be respectively subjected to biaxialstretching to obtain a multilayer stretched injection molded article.The biaxial stretching may be conducted using an ordinary blow moldingmachine.

For example, using a biaxial stretch blow molding machine, the injectionmolded article heated for a period of from about 15 s to about 55 minusing a far infrared heater, etc., is blow-molded using a stretch rodunder a pressure of from 0.5 to 3.5 MPa to obtain the multilayerstretched injection molded article.

The multilayer injection molded articles I and II of the presentinvention may also be produced from a recycled material obtained byre-melting burrs and defective moldings. In this case, from theviewpoint of a good strength of the resulting multilayer injectionmolded article, the recycled material may be suitably used for layersdisposed outside of the layer of the barrier resin composition.

Meanwhile, the respective resin layers may also contain varioussubstances such as lubricants, releasing agents, antioxidants,processing stabilizers, heat stabilizers, ultraviolet absorbers,phyllosilicates, nucleating agents, and inorganic or organic salts andcomplexes of metals such as Co, Mn and Zn unless the addition thereofadversely affects the aimed effects of the present invention.

The single-layer injection molded article of the present invention is inthe form of a molded article containing the polyolefin (C) in which atleast a part of the polyamide resin (A) is dispersed in a layered stateas described above.

The molded article containing the polyolefin (C) is produced from amixed polyolefin (E) containing 40 to 100% by mass of the polyolefin (C)and 60 to 0% by mass of the modified polyolefin (B) and preferablycontaining 50 to 90% by mass of the polyolefin (C) and 10 to 50% by massof the modified polyolefin (B).

The polyamide (A) used in the single-layer injection molded article ofthe present invention may also contain other polyamides such as nylon-6,nylon-66 and nylon-666, ethylene-vinyl alcohol copolymer resins, vinylalcohol-based copolymer resins, acrylonitrile resins, etc., if required.

More specifically, the single-layer injection molded article of thepresent invention is in the form of a molded article having asingle-layer structure which is obtained by melting and mixing the mixedpolyolefin (E) and the polyamide resin (A) and then subjecting theresulting mixture to injection molding. The obtained single-layerinjection molded article contains 40 to 90% by mass of the mixedpolyolefin (E) and 60 to 10% by mass of the polyamide resin (A);preferably contains 50 to 85% by mass of the component (E) and 50 to 15%by mass of the component (A); more preferably contains 55 to 80% by massof the component (E) and 45 to 20% by mass of the component (A); andstill more preferably contains 55 to 75% by mass of the component (E)and 45 to 25% by mass of the component (A) on the basis of a totalamount of the components (E) and (A). When adjusting the content of thecomponent (E) in the single-layer injection molded article to 40% bymass or more, the resulting molded article exhibits an excellentstrength, whereas when adjusting the content of the component (E) to 90%by mass or less, the resulting molded article exhibits a sufficientbarrier property.

The respective resins used for production of the single-layer injectionmolded article of the present invention may be previously melt-kneadedby an extruder, or may be dry-blended together before injection-molded.

The single-layer injection molded article of the present invention mayalso be produced by using a conventionally known injection moldingmachine. The average thickness of a single layer constituting thesingle-layer injection molded article of the present invention ispreferably from 0.1 to 5.0 mm and more preferably from 0.2 to 4 mm.

In the single-layer injection molded article of the present invention,at least a part of the polyamide resin (A) is dispersed therein in alayered state. In particular, it is preferred that the polyamide resin(A) be oriented and dispersed in a layered state in a surface layerportion of the molded article.

In the single-layer injection molded article of the present invention, arecycled material which is obtained by re-melting burrs or defectivemoldings may be introduced as a recycled layer into the molded article.In this case, it is preferred that the amounts of the respective resinsadded be suitably adjusted from the viewpoint of a good strength of theresulting molded article.

Meanwhile, the mixed polyolefin (E) or the polyamide resin (A) used inthe single-layer injection molded article of the present invention mayalso contain various substances such as lubricants, releasing agents,antioxidants, processing stabilizers, heat stabilizers, ultravioletabsorbers, phyllosilicates, nucleating agents, and inorganic or organicsalts and complexes of metals such as Co, Mn and Zn unless the additionthereof adversely affects the aimed effects of the present invention.

The multilayer injection molded articles I and II and the single-layerinjection molded article thus obtained according to the presentinvention are excellent in gas-barrier property and suitably used ascontainer for storing and preserving various products therein. Examplesof the products stored or preserved in these molded articles includeliquid beverages such as carbonated beverage, juice, water, milk, sake,whisky, shochu, coffee, tea, jelly beverage and healthy beverage,seasonings such as liquid seasoning, sauce, soy sauce, dressing, liquidsoup stock, mayonnaise, miso and grated spices, pasty foodstuffs such asjam, cream and chocolate paste, liquid foodstuffs, typically, liquidprocessed foodstuffs such as liquid soup, cooked food, pickles and stew,raw or boiled noodles such as buckwheat noodle, wheat noodle and Chinesenoodle, uncooked or boiled rice such as polished rice, water-conditionedrice and washing-free rice, processed rice products such as boiled ricemixed with fish and vegetables, rice boiled together with red beans andrice gruel, high water content foodstuffs, typically powdery seasoningssuch as powdery soup and powdery soup stock, and low water contentfoodstuffs such as typically dehydrated vegetables, coffee beans, coffeepowder, roasted tea, confectioneries made of cereals, as well as solidand solution chemicals such as agricultural chemicals and insecticides,liquid or pasty drugs, beauty wash, cosmetic cream, milky lotion, hairdressing, hair dye, shampoo, soap and detergent.

EXAMPLES

The present invention will be described in more detail below byreferring to the following examples, etc. In the following examples,etc, various properties of the polyamide resins (A) and the injectionmolded articles were measured and evaluated by the following methods.

(1) Relative Viscosity of Polyamide Resin (A)

One gram of the polyamide resin (A) was accurately weighed, anddissolved in 100 mL of 96% by mass sulfuric acid at a temperature of 20to 30° C. while stirring. After completely dissolving the polyamideresin in the acid, 5 cc of the resulting polyamide solution was rapidlysampled and placed in a Canon Fenske viscometer. After the viscometerfilled with the polyamide solution was allowed to stand in a constanttemperature oven maintained at 25° C. for 10 min, a dropping time (t) ofthe solution was measured. Also, a dropping time (t₀) of the 96% by masssulfuric acid solely was measured. The relative viscosity of thepolyamide resin (A) was calculated from the thus measured dropping timest and t₀ according to the following formula:

Relative Viscosity=(t)/(t ₀)

(2) Extrudiability of Barrier Resin Composition

The respective resin pellets of the barrier resin composition weredry-blended together, charged into a twin-screw extruder equipped with astrong-kneading type screw having a retention section with reversekneading elements, and then kneaded and extruded therefrom under theconditions including a temperature of 260° C., an extrusion output of 10kg/h and a rotating speed of 100 rpm to evaluate an extrusion stabilityof the resin composition according the following ratings.

a: Stably extruded;

b: Slightly unstable; and

c: Unstable.

(3) Moldability of Multilayer Injection Molded Article

A barrel portion of a multilayer injection molded container was cut toevaluate a uniformity of thickness of a layer of the barrier resincomposition according the following ratings.

a: Uniform thickness

b: Slight unevenness in thickness; and

c: Considerable unevenness in thickness.

(4) Delamination Resistance <Multilayer Injection Molded Article>

A barrel portion of a multilayer injection molded container was cut intoan annular sliced piece, and the layer of the barrier resin compositionin the sliced piece was peeled off from the outer layer to evaluate adelamination condition thereof according the following ratings.

a: Large resistance to delamination upon peeling;

b: Slight resistance to delamination upon peeling; and

c: No resistance to delamination upon peeling.

<Multilayer Stretched Injection Molded Article>

The multilayer stretched injection molded article was collapsed at itsbarrel portion three times to observe a delamination condition betweenthe layer of the barrier resin composition and the outer layer by nakedeyes and evaluate the delamination condition according the followingratings.

a: No delamination;

b: Slight delamination; and

c: Considerable delamination.

(5) Oxygen-Barrier Property (Oxygen Permeability)

The oxygen permeability of the injection molded container was measuredat 23° C. under such an atmosphere in which a relative humidity insideof the container was 60% and a relative humidity outside of thecontainer was 50%, according to ASTM D3985. The measurement wasconducted using “OX-TRAN 10/50A” available from Modern Controls Corp.

(6) Heat Resistance of Multilayer Injection Molded Article

The multilayer injection molded container was filled with 20 mL ofwater, or the multilayer stretched injection molded container was filledwith 500 mL of water. After capped, the container was placed in anautoclave available from Tommy Industry, Co., Ltd., and subjected toretort treatment at 90° C. for 30 min. Then, the container was observedby naked eyes to evaluate a degree of deformation of the containeraccording the following ratings.

a: No deformation;

b: Slight deformation; and

c: Considerable deformation.

(7) Dispersing Condition in Single-Layer Injection Molded Article

The resulting single-layer injection molded container was cut along asection thereof, and a dilute iodine available from Tsukishima YakuhinCo., Ltd., was applied to the section of the container to dye thepolyamide therein. Thereafter, the dispersing condition of the polyamidein the resin material of the container was observed using a microscope.The dispersing condition of the polyamide was evaluated as “layeredstate” in the case where the polyamide was dispersed in the form of alayer in a surface layer portion of the molded article, and as“granulated state” in the case where the polyamide was dispersed in theform of granules as a whole.

Production Process A (Production of Multilayer Injection Molded Article)

Using an injection molding machine “Model M200” (four-shot type)available from Meiki Seisakusho Co., Ltd., a three-layer injectionmolded article as a parison having a whole length of 95 mm, an outerdiameter of 22 mm and a wall thickness of 4.0 mm was produced.

(Molding Conditions for Production of Three-Layer Injection MoldedArticle)

Skin-side injection cylinder temperature: 240° C.

Core-side injection cylinder temperature: 260° C.

Resin temperature in flow path within mold: 260° C.

Temperature of mold cooling water: 15° C.

Proportion of barrier resin composition in multilayer injection moldedcontainer: 20% by mass

Production Process B (Production of Multilayer Stretched InjectionMolded Article)

The parison in the form of the three-layer injection molded articleobtained in the above Production Process A was subjected to biaxialstretch blow molding using a blow molding machine “Model: LB-01”available from KRUPP CORPOLAST CORP., to produce a three-layer stretchedinjection molded container (bottle) having the following shape.

Shape: whole length: 223 mm; outer diameter: 65 mm; inner capacity: 500mL; layer structure: polypropylene layer/barrier resinlayer/polypropylene layer=0.12 mm/0.06 mm/0.12 mm; bottom shape:champagne type.

(Conditions of Biaxial Stretch Blow Molding)

Parison heating temperature: 160° C.

Blow pressure: 1.5 MPa

Production Process C (Production of Multilayer Injection MoldedContainer)

Using an injection molding machine “Model M200” (four-shot type)available from Meiki Seisakusho Co., Ltd., a three-layer injectionmolded article as a parison having a whole length of 95 mm, an outerdiameter of 25 mm and a wall thickness of 3.0 mm was produced.

(Molding Conditions for Production of Three-Layer Injection MoldedArticle)

Skin-side injection cylinder temperature: 240° C.

Core-side injection cylinder temperature: 260° C.

Resin temperature in flow path within mold: 260° C.

Temperature of mold cooling water: 15° C.

Proportion of barrier resin composition in multilayer injection moldedarticle: 10% by mass

Production Process D (Production of Single-Layer Injection MoldedContainer)

Using an injection molding machine “Model M200” (four-shot type)available from Meiki Seisakusho Co., Ltd., a single-layer injectionmolded article as a parison having a whole length of 95 mm, an outerdiameter of 22 mm and a wall thickness of 4.0 mm was produced.

(Molding Conditions for Production of Injection Molded Article)

Skin-side injection cylinder temperature: 240° C.

Core-side injection cylinder temperature: 260° C.

Resin temperature in flow path within mold: 260° C.

Temperature of mold cooling water: 15° C.

Production Example 1 (Production of Polyamide Resin: A4)

A jacketed 50-L reaction vessel equipped with a stirrer, a partialcondenser, a cooler, a dropping tank and a nitrogen gas inlet pipe wascharged with 14.2 kg (97.1 mol) of adipic acid and 1.0 kg (6.2 mol) ofisophthalic acid which were previously accurately weighed, and then aninside of the reaction vessel was fully purged and replaced withnitrogen. While further flowing a small amount of nitrogen through thereaction vessel, the contents therein were uniformly melted at 160° C.to form a uniform slurry of the molten adipic acid and isophthalic acid.Then, 14.0 kg (102.6 mol) of m-xylylenediamine was continuously droppedinto the obtained slurry over 1 h under stirring. During the dropping,an inside temperature of the reaction vessel was continuously raised to247° C. Water distilled off during the dropping of m-xylylenediamine wasdischarged out of the reaction system through the partial condenser andthe cooler. After completion of dropping the m-xylylenediamine, theinside temperature of the reaction vessel was raised to 260° C. at whichthe reaction was continued for 1 h. The resultant polymer was withdrawnin the form of strands from the reaction vessel through a nozzle fittedto a lower portion thereof, water-cooled and then cut into pellets.

Next, a heater of a rotary drum type made of stainless steel was chargedwith the thus obtained pellets, and operated at a rotating speed of 10rpm. Then, an inside of the reaction vessel was fully purged andreplaced with nitrogen, and while further flowing a small amount ofnitrogen through the reaction vessel, the temperature inside of thereaction system was raised from room temperature to 150° C. When thetemperature inside of the reaction system reached 150° C., the pressureof the reaction system was reduced to 1 Torr or less, and thetemperature inside of the reaction system was further raised to 210° C.over 110 min. From the time at which the temperature inside of thereaction system reached 210° C., the reaction was continued at the sametemperature for 180 min. After completion of the reaction, the pressurereduction was terminated, and the temperature inside of the reactionsystem was decreased under a nitrogen gas flow. When reaching 60° C.,the pellets were withdrawn from the heater, thereby obtaining apolyamide resin: A4. As a result, it was confirmed that the thusobtained polyamide resin: A4 had a relative viscosity of 2.7 and amelting point of 232° C.

Examples 1 to 3 and Comparative Examples 1 to 3

Using the materials shown in Table 1, a multilayer molded container(parison) having a three-layer structure was produced by the aboveProduction Process A to evaluate a delamination resistance, anoxygen-barrier property and a heat resistance thereof. The results areshown in Table 1. Meanwhile, the multilayer molded containers obtainedin Comparative Examples 2 and 3 easily suffered from delaminationbetween the barrier resin composition layer and the adjacent layers, andwere therefore not subjected to evaluation of an oxygen-barrier propertyand a heat resistance thereof.

Examples 4 to 7 and Comparative Examples 4 and 5

Using the materials shown in Table 2, a multilayer stretched moldedcontainer (bottle) having a three-layer structure was produced by theabove Production Process B to evaluate a delamination resistance, anoxygen-barrier property and a heat resistance thereof. The results areshown in Table 2.

Examples 8 to 12 and Comparative Examples 6 to 9

Using the materials shown in Table 3, a multilayer molded container(parison) having a three-layer structure was produced by the aboveProduction Process C to evaluate an extrudability, a moldability, adelamination resistance, an oxygen-barrier property and a heatresistance thereof. The results are shown in Table 3. Meanwhile, themultilayer molded container obtained in Comparative Example 7 easilysuffered from delamination between the barrier resin composition layer(intermediate layer) and the adjacent layers, and was therefore notsubjected to evaluation of an oxygen-barrier property and a heatresistance thereof.

Examples 13 to 19 and Comparative Examples 10 and 11

Using the materials shown in Table 4, a single-layer injection moldedcontainer (parison) was produced by the above Production Process D toevaluate a dispersibility and an oxygen-barrier property thereof. Theresults are shown in Table 4.

TABLE 1 Comparative Examples Examples 1 2 3 1 2 3 Structure ofmultilayer injection molded article (3-layered) (% by mass) Inner layerand outer layer (polyolefin) C1 (NOVATEC PP-MG03E) 100 100 100 100 100100 Intermediate layer (barrier resin composition) (Polyamide resin) A1(MX NYLON S6121) 40 50 40 100 A2 (MX NYLON S6007) A3 (MX NYLON S6001) 80A4 (Production Example 1) (Modified polyolefin) B1 (MODIC AP-P502) 60 5050 B2 (MODIC AP-P565) 20 (Polyolefin) C2 (NOVATEC PP-M06A) 10 100Evaluation of multilayer injection molded article (3-layered) (4)Delamination resistance a a a a c c (5) Oxygen-barrier property: 0.0180.005 0.017 0.042 — — oxygen permeability (cc/bottle · day · 0.21 atm)(6) Heat resistance a a a a — —

TABLE 2 Comparative Examples Examples 4 5 6 7 4 5 Structure ofmultilayer stretched injection molded article (3-layered) (% by mass)Inner layer and outer layer (polyolefin) C1 (NOVATEC PP-MG03E) 100 100100 100 100 100 Intermediate layer (barrier resin composition)(Polyamide resin) A1 (MX NYLON S6121) 5 A2 (MX NYLON S6007) A3 (MX NYLONS6001) A4 (Production Example 1) 60 40 20 10 (Modified polyolefin) B1(MODIC AP-P502) B2 (MODIC AP-P565) 40 30 80 90 95 (Polyolefin) C1(NOVATEC PP-MG03E) 30 100 Evaluation of multilayer stretched injectionmolded article (3-layered) (4) Delamination resistance a a a a a a (5)Oxygen-barrier property: 0.1 0.3 1.2 1.4 2.0 1.6 oxygen permeability(cc/bottle · day · 0.21 atm) (6) Heat resistance a a a a a a

TABLE 3 Examples 8 9 10 11 12 Structure of multilayer injection moldedarticle (3-layered) (% by mass) Inner layer and outer layer (polyolefin)C1 100 100 100 100 100 (NOVATEC PP-MG03E) Intermediate layer (barrierresin composition) (Polyamide resin) A1 (MX NYLON S6121) 70 70 A4 70 7060 (Production Example 1) (Modified polyolefin) B2 (MODIC AP-P565) 20 1020 20 20 (Polyolefin) C1 (NOVATEC PP-MG03E) (m-Xylylene group-freepolyamide resin) D1 10 20 10 20 (UBE NYLON-1030B) D2 10 (UBENYLON-1024B) Evaluation of multilayer injection molded article(3-layered) (2) Extrudability b b b a b (3) Moldability a a a a a (4)Delamination a b a a a resistance (5) Oxygen-barrier 0.004 0.007 0.0090.010 0.011 property: oxygen permeability (cc/bottle · day · 0.21 atm)(6) Heat resistance a a a a a Comparative Examples 6 7 8 9 Structure ofmultilayer injection molded article (3-layered) (% by mass) Inner layerand outer layer (polyolefin) C1 (NOVATEC PP-MG03E) 100 100 100 100Intermediate layer (barrier resin composition) (Polyamide resin) A1 (MXNYLON S6121) 80 100 A4 (Production Example 1) 20 (Modified polyolefin)B2 (MODIC AP-P565) 20 20 (Polyolefin) C1 (NOVATEC PP-MG03E) 100(m-Xylylene group-free polyamide resin) D1 (UBE NYLON-1030B) D2 (UBENYLON-1024B) 60 Evaluation of multilayer injection molded article(3-layered) (2) Extrudability c a a a (3) Moldability c a a b (4)Delamination resistance a c a a (5) Oxygen-barrier property: 0.014 —0.052 0.020 oxygen permeability (cc/bottle · day · 0.21 atm) (6) Heatresistance a — a a

TABLE 4 Examples 13 14 15 16 17 Composition of single-layer injectionmolded article (% by mass) (Polyamide resin) A1 (MX NYLON S6121) A2 (MXNYLON S6007) 40 A3 (MX NYLON S6001) 25 20 30 45 A4 (ProductionExample 1) (Modified polyolefin) B3 (ADMER GT6) 10 15 15 15 10 B4 (MODICAP-P502) (Polyolefin) C3 65 (NOVATEC HD-HB431) C4 (NOVATEC 65 55 40HD-HY540) C5 50 (NOVATEC HD-HJ580) C6 (NOVATEC PP-FY6) Evaluation ofsingle-layer injection molded article (5) Oxygen-barrier 0.0015 0.00900.0023 0.0003 0.0069 property: oxygen permeability (cc/bottle · day ·0.21 atm) (7) Dispersing condition Layered Layered Layered LayeredLayered Comparative Examples Examples 18 19 10 11 Composition ofsingle-layer injection molded article (% by mass) (Polyamide resin) A1(MX NYLON S6121) 45 A2 (MX NYLON S6007) A3 (MX NYLON S6001) 25 10 A4(Production Example 1) (Modified polyolefin) B3 (ADMER GT6) 15 20 B4(MODIC AP-P502) 10 (Polyolefin) C3 (NOVATEC 100 HD-HB431) C4 (NOVATEC 70HD-HY540) C5 (NOVATEC HD-HJ580) 40 C6 (NOVATEC PP-FY6) 65 Evaluation ofsingle-layer injection molded article (5) Oxygen-barrier 0.0086 0.00210.029 0.025 property: oxygen permeability (cc/bottle · day · 0.21 atm)(7) Dispersing condition Layered Layered — Granulated

Meanwhile, the meanings of the symbols appearing in Tables 1 to 4 are asfollows.

(Polyamide Resin)

-   A1: Polyamide MXD6 having a relative viscosity of 3.8 (“MX NYLON    S6121” available from Mitsubishi Gas Chemical Co., Inc.; polyamide    resin produced from m-xylylenediamine and adipic acid)-   A2: Polyamide MXD6 having a relative viscosity of 2.6 (“MX NYLON    S6007” available from Mitsubishi Gas Chemical Co., Inc.; polyamide    resin produced from m-xylylenediamine and adipic acid)-   A3: Polyamide MXD6 having a relative viscosity of 2.1 (“MX NYLON    S6001” available from Mitsubishi Gas Chemical Co., Inc.; polyamide    resin produced from m-xylylenediamine and adipic acid)-   A4: Polyamide resin obtained in Production Example 1

(Modified Polyolefin)

-   B1: “MODIC AP-P502” (available from Mitsubishi Chemical Corp.;    MFR=1.3; density=0.89)-   B2: “MODIC AP-P565” (available from Mitsubishi Chemical Corp.;    MFR=5.7; density=0.89)-   B3: “ADMER GT6” (available from Mitsui Chemical Corp.; MFR=0.9)-   B4: “MODIC AP-P502” (available from Mitsubishi Chemical Corp.;    MFR=1.3)

(Polyolefin)

-   C1: “NOVATEC MG03E” (polypropylene available from Nippon Polypro    Co., Ltd.; random polymer; MFR=30)-   C2: “NOVATEC PP-M06A” (homopolypropylene available from Nippon    Polypro Co., Ltd.; MFR=60)-   C3: “NOVATEC HD-HB431” (polyethylene available from Nippon    Polyethylene Co., Ltd.; MFR=0.35; density: 0.96)-   C4: “NOVATEC HD-HY540” (polyethylene available from Nippon    Polyethylene Co., Ltd.; MFR=1.0; density: 0.96)-   C5: “NOVATEC HD-HJ580” (polyethylene available from Nippon    Polyethylene Co., Ltd.; MFR=12; density: 0.96)-   C6: “NOVATEC PP-FY6” (polypropylene available from Nippon Polypro    Co., Ltd.; MFR=2.5; density=0.90)    (m-Xylylene Group-Free Polyamide)-   D 1: “UBE NYLON-1030B” (nylon-6 available from Ube Kosan Co., Ltd.;    relative viscosity=4.1)-   D2: “UBE NYLON-1024B” (nylon-6 available from Ube Kosan Co., Ltd.;    relative viscosity=3.5)

INDUSTRIAL APPLICABILITY

The multilayer injection molded articles I and II of the presentinvention are excellent in barrier property, delamination resistance,heat resistance and appearance, in particular, is prevented fromsuffering from delamination between a barrier resin layer and adjacentlayers even when exposed to severe impact upon transportation or dropthereof, are capable of avoiding occurrence of the delamination eventhough they are not formed into such a shape having less irregular andflexed portions, and therefore exhibit a large freedom of design. Thesingle-layer injection molded article of the present invention isexcellent in barrier property and appearance, and can be produced in aneconomically advantageous manner.

Therefore, the multilayer injection molded articles I and II and thesingle-layer injection molded article are suitably used as containersfor liquid food such as beverages and soups or for food and drugscapable of being subjected to retort treatment, etc.

1. An injection molded article with a multilayer structure comprising atleast one layer of a barrier resin composition comprising (A) 10 to 70%by mass of a polyamide resin comprising a diamine unit 70 mol % or moreof which is one or more m-xylylenediamine units and a dicarboxylic acidunit 70 mol % or more of which is one or more dicarboxylic acid unitscontaining a C₄ to C₂₀ α,ω-linear aliphatic dicarboxylic acid andisophthalic acid at a molar ratio of from 30:70 to 100:0; (B) 90 to 30%by mass of a modified polyolefin; and (C) 0 to 50% by mass of apolyolefin.
 2. An injection molded article with a multilayer structurecomprising at least one layer of a barrier resin composition comprising(A) 50 to 90% by mass of a polyamide resin comprising a diamine unit 70mol % or more of which is one or more m-xylylenediamine units and adicarboxylic acid unit 70 mol % or more of which is one or more adicarboxylic acid units containing a C₄ to C₂₀ α,ω-linear aliphaticdicarboxylic acid and isophthalic acid at a molar ratio of from 30:70 to100:0; (B) 2 to 45% by mass of a modified polyolefin; and (D) 2 to 45%by mass of a m-xylylene group-free polyamide.
 3. An injection moldedarticle comprising (A) 10 to 60% by mass of a polyamide resin comprisinga diamine unit 70 mol % or more of which is one or morem-xylylenediamine units and a dicarboxylic acid unit 70 mol % or more ofwhich is one or more dicarboxylic acid units containing a C₄ to C₂₀α,ω-linear aliphatic dicarboxylic acid and isophthalic acid at a molarratio of from 30:70 to 100:0; and (E) 40 to 90% by mass of a mixedpolyolefin comprising (C) 40 to 100% by mass of a polyolefin and (B) 0to 60% by mass of a modified polyolefin, wherein at least a part of thepolyamide resin (A) is dispersed in a layered state.
 4. The injectionmolded article according to claim 1, wherein the polyamide (A) has arelative viscosity of 2.5 or more as measured at 25° C. in 96% by massconcentrated sulfuric acid as a solvent with a concentration of 1 g/100mL.
 5. The injection molded article according to claim 1, wherein themodified polyolefin (B) is obtained by graft-modifying the polyolefin(C) with an unsaturated carboxylic acid or an anhydride thereof.
 6. Theinjection molded article according to claim 2, wherein the m-xylylenegroup-free polyamide (D) is an aliphatic polyamide selected from thegroup consisting of nylon-6, nylon-66 and nylon-666.
 7. The injectionmolded article according to claim 2, wherein the m-xylylene group-freepolyamide (D) is an aliphatic polyamide having a relative viscosity ofless than 5 as measured at 25° C. in 96% by mass concentrated sulfuricacid as a solvent with a concentration of 1 g/100 mL.
 8. The injectionmolded article according to claim 1, wherein the article has amultilayer structure in which the layer of the barrier resin compositionis sandwiched between thermoplastic resin layers (F) each made of apolyolefin.
 9. The injection molded article according to claim 1,wherein the article is in the form of a multilayer stretched injectionmolded article obtained by subjecting a multilayer injection moldedarticle to biaxial stretch blow molding.
 10. The injection moldedarticle according to claim 2, wherein the polyamide (A) has a relativeviscosity of 2.5 or more as measured at 25° C. in 96% by massconcentrated sulfuric acid as a solvent with a concentration of 1 g/100mL.
 11. The injection molded article according to claim 2, wherein themodified polyolefin (B) is obtained by graft-modifying a polyolefin (C)with an unsaturated carboxylic acid or an anhydride thereof.
 12. Theinjection molded article according to claim 3, wherein the modifiedpolyolefin (B) is obtained by graft-modifying the polyolefin (C) with anunsaturated carboxylic acid or an anhydride thereof.
 13. The injectionmolded article according to claim 2, wherein the article has amultilayer structure in which the layer of the barrier resin compositionis sandwiched between thermoplastic resin layers (F) each made of apolyolefin.
 14. The injection molded article according to claim 2,wherein the article is in the form of a multilayer stretched injectionmolded article obtained by subjecting a multilayer injection moldedarticle to biaxial stretch blow molding.